Successive interference canceling for CMDA

ABSTRACT

Successive interference canceling for CMDA. ICI may result from a signal&#39;s multipath effects, or by filtering/suppression of some of the component energy of the signaling waveforms. Energy component attenuation destroys orthogonality of CDMA symbols thereby causing ICI. An ICF suppresses frequency domain portions (attenuates ingress), but also introduces ICI. Following the ICF, the signal is de-spread, sliced, re-spread and convolved with the ICF echoes (except first tap echoes). Convolving re-spread hard decisions with delayed ICF taps is equivalent to partially re-modulating the first-pass hard decisions to efficiently “add-back-in” the signal energy which was blanked/subtracted by the ICF. Alternatively, parameter estimation de-rotates and re-rotates soft symbols and hard decisions, respectively, compensating for undesirable symbol rotation. The convolved signal is subtracted from a delayed version of the ICF output signal. If desired, this process may be repeated successively to enhance the accuracy of the obtained data decisions in the next stage.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present U.S. Utility Patent Application claims prioritypursuant to 35 U.S.C. §119(e) to U.S. Provisional Patent ApplicationSerial No. 60/394,893, entitled “SUCCESSIVE INTERFERENCE CANCELING FORCMDA,” (Attorney Docket No. BP 2161), filed Jul. 10, 2002, pending,which is hereby incorporated herein by reference in its entirety and ismade part of the present U.S. Utility Patent Application for allpurposes.

[0002] The present U.S. Utility Patent Application is acontinuation-in-part of U.S. Utility Patent Application Ser. No.10/136,059, entitled “CHIP BLANKING AND PROCESSING IN S-CDMA TO MITIGATEIMPULSE AND BURST NOISE AND/OR DISTORTION,” (Attorney Docket No. BP2058), filed Apr. 30, 2002, pending, which is hereby incorporated hereinby reference in its entirety and is made part of the present U.S.Utility Patent Application for all purposes.

TECHNICAL FIELD OF THE INVENTION

[0003] The invention relates generally to communication systems; and,more particularly, it relates to communication receivers employing CodeDivision Multiple Access (CDMA).

BACKGROUND OF THE INVENTION

[0004] Data communication systems have been under continual developmentfor many years. One particular type of communication system, a cablemodem (CM) communication system, has been under continual developmentfor the last several years. There has been development to try to providefor improvements in the manner in which communications between the CMusers and a cable modem termination system (CMTS) is performed. Many ofthese prior art approaches seek to perform and provide broadband networkaccess to a number of CM users.

[0005] CM communication systems are realized when a cable company offersnetwork access, oftentimes Internet access, over the cable. This way,the Internet information can use the same cables because the CMcommunication system puts downstream data, sent from the Internet to anindividual computer having CM functionality, into a communicationchannel having a 6 MHz capacity. The reverse transmission is typicallyreferred to as upstream data, information sent from an individual backto the Internet, and this typically requires even less of the cable'sbandwidth. Some estimates say only 2 MHz are required for the upstreamdata transmission, since the assumption is that most people download farmore information than they upload.

[0006] Putting both upstream and downstream data on the cable televisionsystem requires two types of equipment: a cable modem on the customerend and the CMTS at the cable provider's end. Between these two types ofequipment, all the computer networking, security and management ofInternet access over cable television is put into place. Thisintervening region may be referred to as a CM network segment, and avariety of problems can occur to signals sent across this CM networksegment.

[0007] One particular deficiency that may arise in this CM networksegment is the introduction of multi-path effects where there isinterference from one symbol to another in a delayed, scaled form. Forexample, a scaled and delayed version of one symbol is undesirably addedto other symbols. This can lead to significant degradation inperformance. In CDMA systems, these multi-path effects can be totallydeficient, in that, it may make accurate decoding of the transmitteddata virtually impossible. A number of sources may create thesemulti-path effects, including the communication channel itself, as wellas notch filters and interference canceling filters within acommunication receiver that may seek to minimize the deleterious effectsof a communication channel.

[0008] In synchronous code division multiple access (S-CDMA) systems,several cable modems (CMs) transmit their signals such that thesesignals are received at the CMTS on the same frequency and at the sametime. In order for different CM signals to be separated at the CMTS,each CM spreads its data sequence by a code sequence of wider spectrum.The CMTS receives the sum of all CM signals. To separate a specific CMsignal, the CMTS despreads the received sequence by multiplying it withthe code sequence of the desired CM.

[0009] In order to minimize the inter-code-interference (ICI), thespreading codes are chosen such that they are perfectly orthogonal, whenthey are received in perfect synchronism. In order to guarantee codeorthogonality, the code sequences are often chosen to have cyclic-shiftproperties. To preserve the code orthogonality at the CMTS, transmitequalizers are used by CMs to guarantee a perfect single-path overallchannel seen at the CMTS. The transmit equalizer taps at a specific CMare usually set according to an estimate of the channel between the CMand CMTS, which is estimated during the ranging process.

[0010] In many cases, the received signal at the CMTS is corrupted withstrong narrow-band interference (or ingress). An interference cancelingfiler (ICF) is used to notch out ingress before signal despreading.Although this ICF can mitigate ingress, it can cause considerableperformance degradation, which can be explained as follows. The ICF tapscause inter-symbol-interference (ISI) as they can be viewed as echoes tothe signal. These echoes result in shifted (or delayed) replica of thereceived signal at the CMTS side. This enhances ICI as codes loose theirperfect orthogonality. Moreover, due to the cyclic-shift properties ofthe used orthogonal codes, a shifted replica of one code might resembleanother code to a great extent, which enhances the ICI significantly.The same effect can also be caused by imperfections in the channelestimation ranging process, possible channel variations, as well as thefinite length and precision of the transmit equalizers, all of which canresult in residual echoes in the overall channel seen at the CMTS. Theproblems described herein may arise within a variety of contexts,including both wireless and wired communication systems.

[0011] The effect of ISI in CDMA systems can be extremely problematicand is typically very severe in its magnitude and nature. Because theneighboring codes are typically orthogonal to one another, the ISI lookvery similar to delayed (shifted and scaled) versions of one another.This interference can be highly correlated and very problematic.

[0012] Within Time Division Multiple Access (TDMA) communicationsystems, a common approach to deal with ISI is to employ a DecisionFeedback Equalizer (DFE) type structure. This DFE structure cancompensate for interference that takes the form described above that isdelayed by at least one symbol. For example, before decoding a secondsymbol in TDMA using DFE, a scaled version of the first symbol issubtracted there form. The scaling is based on the determinedcharacterization of the ISI that is attributed to the second symbol fromthe first symbol.

[0013] Within the CDMA context, there is no such way known in the priorart to deal with these effects of multi-path and ISI is a satisfactoryway. In the CDMA context, a signal is spread out over a number of chips.Here, the ISI will vary on a chip by chip basis. When narrowbandinterference is undesirably added to these various chips, it makes thedecoding of the signal nearly impossible. This is because all of thechips need to be received to perform the soft decisions that are usedlater to make hard decisions there from. For example, in an embodimentwhere N chips are used to perform symbol decisions, then all of the 128chips are needed to N chips need to be received before making the symboldecisions of the symbols contained and coded therein. The interferencebetween these chips will be non-causal in the CDMA context. The verymanner in which a CDMA receiver performs decoding of its signals is whatmakes it impossible to use a DFE type structure (as in TDMA) to performthe decoding. Within CDMA, a clean representation of all of the chipsmust be achieved. The very way that a CDMA signal is received willinherently include (in the existence of ISI on the chip level) of oneclean chip with the remaining chips having the ISI. Since CDMA does notdecode a single chip at a time (whereas TDMA may decode a single symbolat a time), this need to decode all of the chips together over arelatively long period of time, for many codes, and sum over all ofthose codes to decode each symbol. Basically, the fact that, in CDMA,many symbols are all decoded at the same time, there is a need for aclean representation of all of the chips of a received signal.

SUMMARY OF THE INVENTION

[0014] Various aspects of the invention can be found in a communicationsystem having a receiver that is operable to support and/or performsuccessive interference canceling (SIC) for CDMA systems. The inventionis operable to mitigate the effects of the inter-code-interference (ICI)that may be introduced within CDMA communication systems. The effects ofinter-code-interference (ICI) may be caused by multi-path effects withina signal received by a communication receiver, or by filtering orsuppression of some of the component energy of the signaling waveforms.The attenuation of some of the component energy in the signals destroysthe perfect orthogonality of the set of CDMA symbols, which results inICI. An interference cancellation filter (ICF) is employed that isfollowed by several chip-level interference-canceling stages (ICfunctional blocks).

[0015] In general, the ICF suppresses or “notch filters” portions of thefrequency domain, which is intended to attenuate ingress, but alsointroduces ICI in the process. Following the ICF, the signal isde-spread, sliced, re-spread and convolved with the ICF echoes (all tapsexcept the first tap). The latter process, convolving re-spread harddecisions with the delayed taps of the ICF, is an equivalent means ofpartially re-modulating the first pass hard decisions to efficiently“add back in” the signal energy which was blanked or subtracted by theICF in the first place. In an alternative embodiment, parameterestimation is used to derotate and rerotate soft symbols and harddecisions, respectively, as is necessary to compensate for anyundesirable symbol rotation within the received signal. The convolvedsignal, or partially remodulated energy, which represents theinterference caused by the ICF if all data decisions were correct, isthen subtracted from a delayed (or buffered) version of the outputsignal of the ICF. If desired, this process of de-spread, slice, andpartial re-modulation of the hard decisions may be repeated successivelyto enhance the accuracy of the obtained data decisions in the nextstage.

[0016] The SIC for CDMA of the invention may be implemented in aparallel or serial fashion. Depending on whether limitations of memoryor hardware is a design directive, the appropriate design may beemployed. For example, where memory is relatively cheap and available,the serial implementation may be preferable; where hardware is cheap,the parallel implementation may be preferable. Generally speaking, anycommunication system that employs CDMA, including S-CDMA, may benefitfrom the functionality provided by the invention.

[0017] The invention may be implemented within any variety ofcommunication systems, including wireless communication systems, wiredcommunication systems, optical communication systems, and/or combinationcommunication systems including one or both of these various types ofcommunication infrastructure.

[0018] In addition, other aspects, advantages and novel features of theinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] A better understanding of the invention can be obtained when thefollowing detailed description of various exemplary embodiments isconsidered in conjunction with the following drawings.

[0020]FIG. 1 is a system diagram illustrating an embodiment of a cablemodem (CM) communication system that is built according to theinvention.

[0021]FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system that is built according to the invention.

[0022]FIG. 3 is a system diagram illustrating an embodiment of acellular communication system that is built according to the invention.

[0023]FIG. 4 is a system diagram illustrating another embodiment of acellular communication system that is built according to the invention.

[0024]FIG. 5 is a system diagram illustrating an embodiment of asatellite communication system that is built according to the invention.

[0025]FIG. 6 is a system diagram illustrating an embodiment of amicrowave communication system that is built according to the invention.

[0026]FIG. 7 is a system diagram illustrating an embodiment of apoint-to-point radio communication system that is built according to theinvention.

[0027]FIG. 8 is a system diagram illustrating an embodiment of a highdefinition television (HDTV) communication system that is builtaccording to the invention.

[0028]FIG. 9 is a system diagram illustrating an embodiment of acommunication system that is built according to the invention. &

[0029]FIG. 10 is a system diagram illustrating another embodiment of acommunication system that is built according to the invention.

[0030]FIG. 11 is a system diagram illustrating an embodiment of a cablemodem termination system (CMTS) system that is built according to theinvention.

[0031]FIG. 12 is a system diagram illustrating an embodiment of a burstreceiver system that is built according to the invention.

[0032]FIG. 13 is a system diagram illustrating an embodiment of aBluetooth™ communication system that is built according to theinvention.

[0033]FIG. 14 is a functional block diagram illustrating an embodimentof successive interference canceling (SIC) functionality for CDMA thatis arranged according to the invention in a parallel implementation.

[0034]FIG. 15 is a functional block diagram illustrating an embodimentof SIC functionality for CDMA that is arranged according to theinvention in a serial implementation.

[0035]FIG. 16 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of QPSK (Quadrature Phase ShiftKeying) modulation.

[0036]FIG. 17 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of 8 PSK (8 Phase Shift Keying)modulation.

[0037]FIG. 18 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of 16 QAM (Quadrature AmplitudeModulation) modulation.

[0038]FIG. 19 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of 16 APSK (Amplitude Phase ShiftKeying) modulation.

[0039]FIG. 20 is a functional block diagram illustrating an embodimentof successive interference canceling (SIC) functionality for CDMA thatis arranged according to the invention in a parallel implementation thatis operable to compensate for rotation.

[0040]FIG. 21 is a functional block diagram illustrating an embodimentof SIC functionality for CDMA that is arranged according to theinvention in a serial implementation that is operable to compensate forrotation.

[0041]FIG. 22 is an operational flow diagram illustrating an embodimentof an SIC method for CDMA that is performed according to the invention.

[0042]FIG. 23 is an operational flow diagram illustrating anotherembodiment of an SIC method for CDMA that is performed according to theinvention.

[0043]FIG. 24 is a diagram illustrating a number of considerations ofwhich iteration(s) to perform rotation correction according to theinvention.

[0044]FIG. 25 shows an embodiment of SIC for CDMA simulation resultsaccording to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0045]FIG. 1 is a system diagram illustrating an embodiment of a CMcommunication system 100 that is built according to the invention. TheCM communication system includes a number of CMs (shown as being used bya CM user #1 111, a CM user #2 115, . . . , and a CM user #n 121) and aCMTS 130. The CMTS 130 is a component that exchanges digital signalswith CMs on a cable network.

[0046] Each of a number of CM users (shown as the CM user #1 111, the CMuser #2 115, . . . , and the CM user #n 121) is operable tocommunicatively couple to a CM network segment 199. A number of elementsmay be included within the CM network segment 199. For example, routers,splitters, couplers, relays, and amplifiers may be contained within theCM network segment 199 without departing from the scope and spirit ofthe invention.

[0047] The CM network segment 199 allows communicative coupling betweena CM user and a cable headend transmitter 120 and/or a CMTS 130. In someembodiments, a cable CMTS is in fact contained within a headendtransmitter. In other embodiments, a cable CMTS is located externallywith respect to a headend transmitter. For example, the CMTS 130 may belocated externally to the cable headend transmitter 120. In alternativeembodiments, a CMTS 135 may be located within the cable headendtransmitter 120. The CMTS 130 may be located at a local office of acable television company or at another location within a CMcommunication system. In the following description, the CMTS 130 is usedfor illustration; yet, the same functionality and capability asdescribed for the CMTS 130 may equally apply to embodiments thatalternatively employ the CMTS 135. The cable headend transmitter 120 isable to provide a number of services including those of audio, video,local access channels, as well as any other service known in the art ofcable systems. Each of these services may be provided to the one or moreCM users 111, 115, . . . , 121.

[0048] In addition, through the CMTS 130, the CM users 111, 115, . . . ,121 are able to transmit and receive data from the Internet, . . . ,and/or any other network to which the CMTS 130 is communicativelycoupled. The operation of a CMTS, at the cable-provider's head-end, maybe viewed as providing analogous functions provided by a digitalsubscriber line access multiplexor (DSLAM) within a digital subscriberline (DSL) system. The CMTS 130 takes the traffic coming in from a groupof customers on a single channel and routes it to an Internet ServiceProvider (ISP) for connection to the Internet, as shown via the Internetaccess. At the head-end, the cable providers will have, or lease spacefor a third-party ISP to have, servers for accounting and logging,dynamic host configuration protocol (DHCP) for assigning andadministering the Internet protocol (IP) addresses of all the cablesystem's users (CM users 111, 115, . . . , 121), and typically controlservers for a protocol called Data Over Cable Service InterfaceSpecification (DOCSIS), the major standard used by U.S. cable systems inproviding Internet access to users. The servers may also be controlledfor a protocol called European Data Over Cable Service InterfaceSpecification (EuroDOCSIS), the major standard used by European cablesystems in providing Internet access to users, without departing fromthe scope and spirit of the invention.

[0049] The downstream information flows to all of the connected CM users111, 115, . . . , 121. The individual network connection, within the CMnetwork segment 199, decides whether a particular block of data isintended for it or not. On the upstream side, information is sent fromthe CM users 111, 115, . . . , 121 to the CMTS 130; on this upstreamtransmission, the users within the CM users 111, 115, . . . , 121 towhom the data is not intended do not see that data at all. As an exampleof the capabilities provided by a CMTS, the CMTS will enable as many as1,000 users to connect to the Internet through a single 6 MHz channel.Since a single channel is capable of 30-40 megabits per second of totalthroughput, this means that users may see far better performance than isavailable with standard dial-up modems. Some embodiments implementingthe invention are described below and in the various Figures that showthe data handling and control within one or both of a CM and a CMTSwithin a CM system that operates by employing S-CDMA (Synchronous CodeDivision Multiple Access).

[0050] The CM users 111, 115, . . . , 121 and the CMTS 130 communicatesynchronization information to one another to ensure proper alignment oftransmission from the CM users 111, 115, . . . , 121 to the CMTS 130.This is where the synchronization of the S-CDMA communication systems isextremely important. When a number of the CMs all transmit their signalsat a same time such that these signals are received at the CMTS 130 onthe same frequency and at the same time, they must all be able to beproperly de-spread and decoded for proper signal processing.

[0051] Each of the CMs users 111, 115, . . . , 121 is located arespective transmit distance from the CMTS 130. In order to achieveoptimum spreading diversity and orthogonality for the CMs users 111,115, . . . , 121 to transmission of the CMTS 130, each of the CMtransmissions must be synchronized so that it arrives, from theperspective of the CMTS 130, synchronous with other CM transmissions. Inorder to achieve this goal, for a particular transmission cycle, each ofthe CMs 111, 115, . . . , 121 will typically transmit to the CMTS 130 ata respective transmission time, which will likely differ from thetransmission times of other CMs. These differing transmission times willbe based upon the relative transmission distance between the CM and theCMTS 130. These operations may be supported by the determination of theround trip delays (RTPs) between the CMTS 130 and each supported CM.With these RTPs determined, the CMs may then determine at what point totransmit their S-CDMA data so that all CM transmissions will arrivesynchronously at the CMTS 130.

[0052] The invention enables successive interference canceling (SIC)functionality for CDMA within the CMTS 130. This SIC functionality forCDMA is shown as within a functional block 131 within the cable headendtransmitter 120. This SIC functionality for CDMA may also be supportedwithin the CMTS 135 and/or the CMTS 130, whichever may be implementedwithin a particular embodiment. All of the functionality describedherein this patent application may be performed within the context ofthe CM communication system of the FIG. 1. The FIG. 1 shows just oneembodiment where the various aspects of the invention may beimplemented. Several other embodiments are described as well.

[0053]FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system 200 that is built according to the invention. Fromcertain perspectives, the FIG. 2 may be viewed as a communication systemallowing bi-directional communication between a customer premiseequipment (CPE) 240 and a network. In some embodiments, the CPE 240 is apersonal computer or some other device allowing a user to access anexternal network. The external network may be a wide area network (WAN)280, or alternatively, the Internet 290 itself. For example, the CMcommunication system 200 is operable to allow Internet protocol (IP)traffic to achieve transparent bi-directional transfer between aCMTS-network side interface (CMTS-NSI: viewed as being between the CMTS230 and the Internet 290) and a CM to CPE interface (CMCI: viewed asbeing between the CM 210 and the CPE 240).

[0054] The WAN 280, and/or the Internet 290, is/are communicativelycoupled to the CMTS 230 via the CMTS-NSI. The CMTS 230 is operable tosupport the external network termination, for one or both of the WAN 280and the Internet 290. The CMTS 230 includes a modulator and ademodulator to support transmitter and receiver functionality to andfrom a CM network segment 299. The receiver functionality within theCMTS 230 is operable to support SIC functionality for CDMA 231 accordingto the invention.

[0055] A number of elements may be included within the CM networksegment 299. For example, routers, splitters, couplers, relays, andamplifiers may be contained within the CM network segment 299 withoutdeparting from the scope and spirit of the invention. The CM networksegment 299 allows communicative coupling between a CM user and the CMTS230.

[0056]FIG. 3 is a system diagram illustrating an embodiment of acellular communication system 300 that is built according to theinvention. A mobile transmitter 310 has a local antenna 311. The mobiletransmitter 310 may be any number of types of transmitters including acellular telephone, a wireless pager unit, a mobile computer havingtransmit functionality, or any other type of mobile transmitter. Themobile transmitter 310 transmits a signal, using its local antenna 311,to a base station receiver 340 via a wireless communication channel. Thebase station receiver 340 is communicatively coupled to a receivingwireless tower 349 to be able to receive transmission from the localantenna 311 of the mobile transmitter 310 that have been communicatedvia the wireless communication channel. The receiving wireless tower 349communicatively couples the received signal to the base station receiver340.

[0057] The base station receiver 340 is then able to support SICfunctionality for CDMA according to the invention, as shown in afunctional block 341, on the received signal. The FIG. 3 shows just oneof many embodiments where SIC functionality for CDMA, performedaccording to the invention, may be performed to provide for improvedoperation within a communication system.

[0058]FIG. 4 is a system diagram illustrating another embodiment of acellular communication system that is built according to the invention.From certain perspectives, the FIG. 4 may be viewed as being the reversetransmission operation of the cellular communication system 300 of theFIG. 3. A base station transmitter 420 is communicatively coupled to atransmitting wireless tower 421. The base station transmitter 420, usingits transmitting wireless tower 421, transmits a signal to a localantenna 439 via a wireless communication channel. The local antenna 439is communicatively coupled to a mobile receiver 430 so that the mobilereceiver 430 is able to receive transmission from the transmittingwireless tower 421 of the base station transmitter 420 that have beencommunicated via the wireless communication channel. The local antenna439 communicatively couples the received signal to the mobile receiver430. It is noted that the mobile receiver 430 may be any number of typesof transmitters including a cellular telephone, a wireless pager unit, amobile computer having transmit functionality, or any other type ofmobile transmitter.

[0059] The mobile receiver 430 is then able to support SIC functionalityfor CDMA according to the invention, as shown in a functional block 431,on the received signal. The FIG. 4 shows just one of many embodimentswhere the SIC functionality for CDMA, performed according to theinvention, may be performed to provide for improved operation within acommunication system.

[0060]FIG. 5 is a system diagram illustrating an embodiment of asatellite communication system 500 that is built according to theinvention. A transmitter 520 is communicatively coupled to a wirednetwork 510. The wired network 510 may include any number of networksincluding the Internet, proprietary networks, . . . , and other wirednetworks. The transmitter 520 includes a satellite earth station 551that is able to communicate to a satellite 553 via a wirelesscommunication channel. The satellite 553 is able to communicate with areceiver 530. The receiver 530 is also located on the earth. Here, thecommunication to and from the satellite 553 may cooperatively be viewedas being a wireless communication channel, or each of the communicationto and from the satellite 553 may be viewed as being two distinctwireless communication channels.

[0061] For example, the wireless communication “channel” may be viewedas not including multiple wireless hops in one embodiment. In otherembodiments, the satellite 553 receives a signal received from thesatellite earth station 551, amplifies it, and relays it to the receiver530; the receiver 530 may include terrestrial receivers such assatellite receivers, satellite based telephones, . . . , and satellitebased Internet receivers, among other receiver types. In the case wherethe satellite 553 receives a signal received from the satellite earthstation 551, amplifies it, and relays it, the satellite 553 may beviewed as being a “transponder.” In addition, other satellites may exist(and operate in conjunction with the satellite 553) that perform bothreceiver and transmitter operations. In this case, each leg of anup-down transmission via the wireless communication channel would beconsidered separately. Clearly, a wireless communication channel betweenthe satellite 553 and a fixed earth station would likely be lesstime-varying than the wireless communication channel between thesatellite 553 and a mobile station.

[0062] In whichever embodiment is implemented, the satellite 553communicates with the receiver 530. The receiver 530 may be viewed asbeing a mobile unit in certain embodiments (employing a local antenna512); alternatively, the receiver 530 may be viewed as being a satelliteearth station 552 that may be communicatively coupled to a wired networkin a similar manner that the satellite earth station 551, within thetransmitter 520, communicatively couples to the wired network 510. Inboth situations, the receiver 530 is able to support SIC functionalityfor CDMA, as shown in a functional block 531, according to theinvention. For example, the receiver 530 is able to perform SICfunctionality for CDMA, as shown in a functional block 531, on thesignal received from the satellite 553. The FIG. 5 shows just one ofmany embodiments where the SIC functionality for CDMA, performedaccording to the invention, may be performed to provide for improvedreceiver and system performance.

[0063]FIG. 6 is a system diagram illustrating an embodiment of amicrowave communication system 600 that is built according to theinvention. A tower transmitter 611 includes a wireless tower 615. Thetower transmitter 611, using its wireless tower 615, transmits a signalto a tower receiver 612 via a wireless communication channel. The towerreceiver 612 includes a wireless tower 616. The wireless tower 616 isable to receive transmissions from the wireless tower 615 that have beencommunicated via the wireless communication channel. The tower receiver612 is then able to support SIC functionality for CDMA, as shown in afunctional block 633. The FIG. 6 shows just one of many embodimentswhere SIC functionality for CDMA, performed according to the invention,may be performed to provide for improved receiver and systemperformance.

[0064]FIG. 7 is a system diagram illustrating an embodiment of apoint-to-point radio communication system 700 that is built according tothe invention. A mobile unit 751 includes a local antenna 755. Themobile unit 751, using its local antenna 755, transmits a signal to alocal antenna 756 via a wireless communication channel. The localantenna 756 is included within a mobile unit 752. The mobile unit 752 isable to receive transmissions from the mobile unit 751 that have beencommunicated via the wireless communication channel. The mobile unit 752is then able to support SIC functionality for CDMA, as shown in afunctional block 753, on the received signal. The FIG. 7 shows just oneof many embodiments where SIC functionality for CDMA, performedaccording to the invention, may be performed to provide for improvedreceiver and system performance.

[0065]FIG. 8 is a system diagram illustrating an embodiment of a highdefinition television (HDTV) communication system 800 that is builtaccording to the invention. An HDTV transmitter 810 includes a wirelesstower 811. The HDTV transmitter 810, using its wireless tower 811,transmits a signal to an HDTV set top box receiver 820 via a wirelesscommunication channel. The HDTV set top box receiver 820 includes thefunctionality to receive the wireless transmitted signal. The HDTV settop box receiver 820 is also communicatively coupled to an HDTV display630 that is able to display the demodulated and decoded wirelesstransmitted signals received by the HDTV set top box receiver 820.

[0066] The HDTV set top box receiver 820 is then able to support SICfunctionality for CDMA, as shown in a functional block 823 to providefor improved receiver performance. The FIG. 8 shows yet another of manyembodiments where SIC functionality for CDMA, performed according to theinvention, may be performed to provide for improved receiver and systemperformance.

[0067]FIG. 9 is a system diagram illustrating an embodiment of acommunication system that is built according to the invention. The FIG.9 shows communicative coupling, via a communication channel 999, betweentwo transceivers, namely, between a transceiver 901 and a transceiver902. The communication channel 999 may be a wired communication channelor a wireless communication channel.

[0068] Each of the transceivers 901 and 902 includes a transmitter and areceiver. For example, the transceiver 901 includes a transmitter 949and a receiver 940; the transceiver 902 includes a transmitter 959 and areceiver 930. The receivers 940 and 930, within the transceivers 901 and902, respectively, are each operable to support SIC functionality forCDMA according to the invention. This will allow improved signalprocessing for both of the transceivers 901 and 902. For example, thereceiver 940, within the transceiver 901, is able to support SICfunctionality for CDMA, as shown in a functional block 941, on a signalreceived from the transmitter 959 of the transceiver 902. Similarly, thereceiver 930, within the transceiver 902, is able to support SICfunctionality for CDMA, as shown in a functional block 931, on a signalreceived from the transmitter 949 of the transceiver 901. The FIG. 9shows yet another of many embodiments where SIC functionality for CDMA,performed according to the invention, may be performed to provide forimproved receiver performance.

[0069]FIG. 10 is a system diagram illustrating another embodiment of acommunication system 1000 that is built according to the invention. TheFIG. 10 shows communicative coupling, via a uni-directionalcommunication channel 1099, between a transmitter 1049 and a receiver1030. The communication channel 1099 may be a wired communicationchannel or a wireless communication channel. The receiver 1030 isoperable to support SIC functionality for CDMA, as shown in a functionalblock 1031, according to the invention. The FIG. 10 shows yet another ofmany embodiments where SIC functionality for CDMA, performed accordingto the invention, may be performed to provide for improved receiver andsystem performance.

[0070]FIG. 11 is a system diagram illustrating an embodiment of a CMTSsystem 1100 that is built according to the invention. The CMTS system1100 includes a CMTS medium access controller (MAC) 1130 that operateswith a number of other devices to perform communication from one or moreCMs to a WAN 1180. The CMTS MAC 1130 may be viewed as providing thehardware support for MAC-layer per-packet functions includingfragmentation, concatenation, and payload header suppression that allare able to offload the processing required by a system centralprocessing unit (CPU) 1172. This will provide for higher overall systemperformance. In addition, the CMTS MAC 1130 is able to provide supportfor carrier class redundancy via timestamp synchronization across anumber of receivers, shown as a receiver 1111, a receiver 1111, and areceiver 1113 that are each operable to receive upstream analog inputs.In certain embodiments, each of the receivers 1111, 1112, and 1113 aredual universal advanced TDMA/CDMA (Time Division Multiple Access/CodeDivision Multiple Access) PHY-layer burst receivers. That is to say,each of the receivers 1111, 1112, and 1113 includes at least one TDMAreceive channel and at least one CDMA receive channel; in this case,each of the receivers 1111, 1112, and 1113 may be viewed as beingmulti-channel receivers. In other embodiments, the receivers 1111, 1112,and 1113 includes only CDMA receive channels. An embodiment of areceiver including only CDMA receive channels is shown in FIG. 12.

[0071] In addition, the CMTS MAC 1130 may be operated remotely with arouting/classification engine 1179 that is located externally to theCMTS MAC 1130 for distributed CMTS applications including mini fibernode applications. Moreover, a Standard Programming Interface (SPI)master port may be employed to control the interface to the receivers1111, 1112, and 1113 as well as to a downstream modulator 1120.

[0072] The CMTS MAC 1130 may be viewed as being a highly integrated CMTSMAC integrated circuit (IC) for use within the various DOCSIS andadvanced TDMA/CDMA physical layer (PHY-layer) CMTS products. The CMTSMAC 1130 employs sophisticated hardware engines for upstream anddownstream paths. The upstream processor design is segmented and usestwo banks of Synchronous Dynamic Random Access Memory (SDRAM) tominimize latency on internal buses. The two banks of SDRAM used by theupstream processor are shown as upstream SDRAM 1175 (operable to supportkeys and reassembly) and SDRAM 1176 (operable to support Packaging,Handling, and Storage (PHS) and output queues). The upstream processorperforms Data Encryption Standard (DES) decryption, fragment reassembly,de-concatenation, payload packet expansion, packet acceleration,upstream Management Information Base (MIB) statistic gathering, andpriority queuing for the resultant packets. Each output queue can beindependently configured to output packets to either a Personal ComputerInterface (PCI) or a Gigabit Media Independent Interface (GMII). DOCSISMAC management messages and bandwidth requests are extracted and queuedseparately from data packets so that they are readily available to thesystem controller.

[0073] The downstream processor accepts packets from priority queues andperforms payload header suppression, DOCSIS header creation, DESencryption, Cyclic Redundancy Check (CRC) and Header Check Sequence (ofthe DOCSIS specification), Moving Pictures Experts Group (MPEG)encapsulation and multiplexing, and timestamp generation on the in-banddata. The CMTS MAC 1130 includes an out-of-band generator and CDMAPHY-layer (and/or TDMA PHY-layer) interface so that it may communicatewith a CM device's out-of-band receiver for control of power managementfunctions. The downstream processor will also use SDRAM 1177 (operableto support PHS and output queues). The CMTS MAC 1130 may be configuredand managed externally via a PCI interface and a PCI bus 1171.

[0074] Each of the receivers 1111, 1112, and 1113 is operable to supportSIC functionality for CDMA. For example, the receiver 1111 is operableto support SIC functionality for CDMA, as shown in a functional block1191; the receiver 1112 is operable to support SIC functionality forCDMA, as shown in a functional block 1192; and the receiver 1113 isoperable to support SIC functionality for CDMA, as shown in a functionalblock 1193. The FIG. 11 shows yet another embodiment in which SICfunctionality for CDMA may be performed according to the invention. Anyof the functionality and operations described in the other embodimentsmay be performed within the context of the CMTS system 1100 withoutdeparting from the scope and spirit of the invention.

[0075]FIG. 12 is a system diagram illustrating an embodiment of a burstreceiver system 1200 that is built according to the invention. The burstreceiver system 1200 includes at least one multi-channel receiver 1210.The multi-channel receiver 1210 is operable to receive a number ofupstream analog inputs that are transmitted from CMs. The upstreamanalog inputs may be in the form of either TDMA (Time Division MultipleAccess) and/or CDMA (Code Division Multiple Access) format. A number ofreceive channels may be included within the multichannel receiver 1210.The FIG. 12 shows a particular embodiment where the multi-channelreceiver 1210 includes a number of CDMA receive channels; however, TDMAreceive channels may also be included.

[0076] For example, the multi-channel receiver 1210 is operable tosupport CDMA receive channels 1220 (shown as CDMA signal 1 and CDMAsignal 2) and to support SIC functionality for CDMA, as shown in afunctional block 1221, for those received CDMA signals. In addition, themulti-channel receiver 1210 is operable to support CDMA receive channels1230 (shown as CDMA signal 3 and CDMA signal 4) and to support SICfunctionality for CDMA, as shown in a functional block 1231, for thosereceived CDMA signals; the multi-channel receiver 1210 is operable tosupport CDMA receive channels 1240 (shown as CDMA signal N and CDMAsignal N−1) and to support SIC functionality for CDMA, as shown in afunctional block 1241, for those received CDMA signals.

[0077] Generically speaking, the multi-channel receiver 1210 is operableto support a number of receive channels and to support SIC functionalityfor CDMA for those received signals. The multi-channel receiver 1210 ofthe FIG. 12 is operable to interface with a CMTS MAC. The burst receiversystem 1200 may include a number of multi-channel receivers that areeach operable to interface with the CMTS MAC.

[0078] In certain embodiments, the multi-channel receiver 1210 providesa number of various functionalities. The multi-channel receiver 1210 maybe a universal headend advanced TDMA PHY-layer QPSK/QAM (QuadraturePhase Shift Keying/Quadrature Amplitude Modulation) burst receiver; themulti-channel receiver 1210 also include functionality to be a universalheadend advanced CDMA PHY-layer QPSK/QAM burst receiver; or themulti-channel receiver 1210 also include functionality to be a universalheadend advanced TDMA/CDMA PHY-layer QPSK/QAM burst receiver offeringboth TDMA/CDMA functionality. The multichannel receiver 1210 may beDOCSIS/EuroDOCSIS based, IEEE 802.14 compliant. The multi-channelreceiver 1210 may be adaptable to numerous programmable demodulationincluding BPSK (Binary Phase Shift Keying), and/or QPSK,8/16/32/64/128/256/516/1024 QAM. The multi-channel receiver 1210 isadaptable to support variable symbols rates as well. Other functionalitymay likewise be included to the multi-channel receiver 1210 withoutdeparting from the scope and spirit of the invention. Such variationsand modifications may be made to the communication receiver.

[0079] While a particular embodiment of a burst receiver system 1200 isillustrated within the FIG. 12, it is also noted that a continuousreceiver will also support SIC functionality for CDMA according to theinvention. In general, any CDMA receiver may be adapted to support theSIC functionality for CDMA according to the invention.

[0080]FIG. 13 is a system diagram illustrating an embodiment of aBluetooth™ TM communication system 1300 that is built according to theinvention. The Bluetooth™ wireless technology is an open specificationfor a small-form-factor, low-cost, personal area network connectionamong mobile computers, mobile phones and other devices. The Bluetooth™wireless technology specification provides secure, radio-basedtransmission of data and voice. It delivers opportunities for rapid, adhoc, automatic, wireless connections, even when devices are not withinthe line of sight. The Bluetooth™ wireless technology uses a globallyavailable frequency range to ensure interoperability no matter where youtravel.

[0081] Bluetooth™ is a standard for a small, cheap radio chip to beplugged into computers, printers, mobile phones, etc. A Bluetooth™ chipis designed to replace cables by taking the information normally carriedby the cable, and transmitting it at a special frequency to a receiverBluetooth™ chip, which will then give the information received to thecomputer, phone whatever. In certain embodiments, Bluetooth™communicates on a frequency of 2.45 gigahertz (GHz), which has been setaside by international agreement for the use of industrial, scientificand medical devices (ISM).

[0082] The Bluetooth™ wireless technology was developed by theBluetooth™ Special Interest Group, which was founded in 1998 to definean industry-wide specification for connecting personal and businessmobile devices. More than 1,400 companies are now members of the SpecialInterest Group, signifying the industry's unprecedented acceptance ofthe Bluetooth™ wireless technology.

[0083] The FIG. 13 shows a Bluetooth™ operable device that is operableto communicate with another device via a wireless communication channel.The Bluetooth™ operable device may be a computer, printer, and/or mobilephone (or other device) without departing from the scope and spirit ofthe invention. Specifically, the FIG. 13 shows a single chip Bluetooth™2.4 GHz transceiver and baseband device 1310 that is operable to supportSIC functionality for CDMA as shown in a functional block 1311. Fromcertain perspectives, the single chip Bluetooth™ 2.4 GHz transceiver andbaseband device 1310 may be viewed as being a complete single chipBluetooth™ compliant, single chip solution that integrates the 2.4 GHzfractional-N radio transceiver and baseband controller. The 2.4 GHzfractional-N radio transceiver portion is operable to receive a clocksignal from an external clock (say, from a mobile unit) in certainembodiments. The single chip Bluetooth™ 2.4 GHz transceiver and basebanddevice 1310 will provide for a wide range of wireless communication andnetworking applications, including mobile phones, PCs, laptops, PDAs,and other peripheral devices. The other device may be a Bluetooth™device 1350, that may also be operable to support SIC functionality forCDMA as shown in a functional block 1351.

[0084] In certain embodiments, a radio section of the single chipBluetooth™ 2.4 GHz transceiver and baseband device 1310 incorporates thecomplete receive and transmit paths, including PLL, VCO, LNA, PA,up-converter, down-converter, modulator, demodulator, and channel selectfiltering.

[0085] The baseband section of the single chip Bluetooth™ 2.4 GHztransceiver and baseband device 1310 controls all Bluetooth™functionality from the PHY radio to the HCI layer. This includes allbit-level processing, event scheduling, voice/data flow, and on-chipUSB/UART/Audio PCM interfaces (as provided by a USB Port 1321 and a UARTPort 1322 that may communicatively couple to a host processor 1331, by aPCM Port 1323 that may communicatively couple to an audio CODEC 1332).In addition, the single chip Bluetooth™ 2.4 GHz transceiver and basebanddevice 1310 is also operable to communicatively couple to an (optional)flash memory via a processor bus 1323.

[0086] The single chip Bluetooth™ 2.4 GHz transceiver and basebanddevice 1310 is a monolithic component implemented in a standard digitalCMOS process, and requires minimal external components to provide alow-cost BOM solution.

[0087] It is noted that the single chip Bluetooth™ 2.4 GHz transceiverand baseband device 1310 within the FIG. 13 shows yet another embodimentof device that is operable to support SIC functionality for CDMAaccording to the invention. Clearly, other Bluetooth™ communicationsystems may also be adapted to support the SIC functionality for CDMA aswell.

[0088]FIG. 14 is a functional block diagram illustrating an embodimentof successive interference canceling (SIC) functionality for CDMA 1400that is arranged according to the invention in a parallelimplementation. In a block 1401, a spread signal is received from anelement 1401 that has undesirably introduced multipath interference.This multipath interference may be caused by a variety of sources. Forexample, one source of the multipath interference may be from theeffects of the communication channel itself as shown in a block 1404.However, other elements that may be employed to compensate for theexistence of narrowband interference within a signal received by acommunication receiver; sometimes, these introduced elements actuallywill introduce some degree of multipath interference. For example, someelements that are employed to minimize the effects of ingress and/ornarrowband interference may include an interference cancellation filter(ICF) 1402 and/or an interference notch filter 1403. The multipathinterference element 1401 may be viewed, at the very least, as being anelement that introduces multi-path effects into the signal received bythe SIC functionality for CDMA 1400. The attenuation of some of thecomponent energy in the signals destroys the perfect orthogonality ofthe set of CDMA symbols, which results in ICI. In general, the ICFsuppresses or “notch filters” portions of the frequency domain, which isintended to attenuate ingress, but also introduces ICI in the process.

[0089] The FIG. 14 shows a functional block diagram of the parallelimplementation of the invention. In this approach, two or moresuccessive interference canceling (SIC) stages are shown by the ICfunctional blocks. The approach also employs a buffer of size M, whichshould be adequate to store the output of the ICF till despread, slice,re-spread, and convolution operations are done. The ICF taps are chosento notch out (or “blank”) any present ingress in the signal. Thecomputation of these taps may be performed using any approach known inthe art.

[0090] For example, the signal output by the multipath interferenceelement 1401 is simultaneously provided to an interference cancellation(IC) functional block 1410 and a delay element Z^(−M) 1491. Whenmultiple iterations of ICF are to performed using the SIC functionalityfor CDMA 1400, . . . the output of the multipath interference element1401 is also simultaneously provided to a delay element Z^(−(N−1)M) 1492(when multiple iterations are performed), and to a delay element Z^(−NM)1492 (when N iterations are performed). The output of the IC functionalblock 1410 may be selected when there is no multipath interference inthe received signal whatsoever. The IC functional block 1410 includes adespread functional block 1411, a slicer 1412, a re-spread functionalblock 1413, and an ICF-1 functional block 1414 (to perform convolutionoperations) according to the invention.; the ICF-1 functional blocksdescribed herein may also be referred to as convolution functionalblocks.

[0091] The despread functional block 1411 generates the soft decision ofthe received signal. The slicer 1412 makes a hard decision based on thesoft decision provided by the despread functional block 1411. These harddecisions by the slicer 1412 make the decisions offline with no cleaningof the signal; that is to say, without removing any ISI that existsamong the chips. These hard decisions may include a number of errorsthat would be too significant within data applications, but they willgive some accuracy of the received data even though there may be manyerror contained therein. This initial estimate of the data is thenre-spread, in the functional block 1413, to reconstruct the chip levelISI. Then, the operation within the ICF-1 functional block 1414generates the reconstructed ISI (on a chip level) of all of the othertaps besides this first tap.

[0092] The functional operations of the functional blocks 1413 and 1414together, is described as partially re-modulating the hard decisions inU.S. Utility patent application Ser. No. 10/136,059, entitled “CHIPBLANKING AND PROCESSING IN S-CDMA TO MITIGATE IMPULSE AND BURST NOISEAND/OR DISTORTION,” (Attorney Docket No. BP 2058). This is also true forother embodiments described herein that perform similar functionality asthe functional blocks 1413 and 1414.

[0093] This result may then be subtracted from the output of the delayelement Z^(−M) 1491. The delay length of the buffer, delay elementZ^(−M) 1491, is sufficient to match substantially the time required toperform the operations within each of the elements of the IC functionalblock 1410.

[0094] This chain of IC functionality may be repeated successively ifdesired to provide for even further improved performance. For example,the output of the node (the first summing node) where the output of thedelay element Z^(−M) 1491 and the negative output of the IC functionalblock 1410 are summed together may be fed into an IC functional block1420. The IC functional block 1420 will include comparable elements ofthe IC functional block 1410. For example, the IC functional block 1420includes a despread functional block 1421 that generates soft decisionof the output from the first summing node. A slicer 1422 makes a harddecision based on the soft decision provided by the despread functionalblock 1421. These hard decisions by the slicer 1422 make the decisionsoffline with an improved, cleaner signal; that is to say, some of theISI that exists among the chips will have been removed by the operationsdescribed above. These hard decisions will include a fewer number oferrors than in the previous chain of IC functionality. This next 2^(nd)order initial estimate of the data is then re-spread, in a functionalblock 1423, to reconstruct the chip level ISI (which will be reducedwhen compared to the previous chain).

[0095] Then, the operation within an ICF-1 functional block 1424generates the reconstructed ISI (on a chip level) of all of the othertaps besides this first tap. Functional blocks 1423 and 1424 constitutethe generation of the partial re-modulated energy described in U.S.Utility patent application Ser. No. 10/136,059, entitled “CHIP BLANKINGAND PROCESSING IN S-CDMA TO MITIGATE IMPULSE AND BURST NOISE AND/ORDISTORTION,” (Attorney Docket No. BP 2058).

[0096] Again, this reconstructed ISI will be relatively less than in thefirst chain. This result may then be subtracted from the output of adelay element Z^(−(N−1)M) 1492. The delay length of the buffer, delayelement Z^(−(N−1)M) 1492, is sufficient to match substantially the timerequired to perform the operations within each of the elements of the ICfunctional block 1410, within each of the elements of the IC functionalblock 1420, and any additional IC functional blocks that are employed.

[0097] It is noted that the resultant output of the slicer 1412 withinthe IC functional block 1410 may be selected as an output.Alternatively, the resultant output of the slicer 1422 within the ICfunctional block 1420 may be selected as an output when it has beendetermined that a solution has been reached (say when a differencebetween potential output 0 and potential output 1 are within apredetermined degree of magnitude). Alternatively, this potential output1 may be selected when a predetermined number of chains (2 in such anembodiment) are selected to be performed. Another method of determiningwhen to end this process is to look at the Signal to Noise Ratio (SNR)of the signal and to select the output from one of the stages when theSNR meets a predetermined threshold.

[0098] Subsequent chains may be implemented successively as desired toprovide even further performance. For example, multiple chains may beincluded up to an IC functional block 1430 (having a de-spreadfunctional block 1431, a slicer 1432, a re-spread functional block 1433,and an ICF-1 functional block 1434) may also be employed when they arepreceded by the appropriate delay stages. The outputs of each of theslicers 1412, 1422, . . . , and 1432 (within the IC functional blocks1410, 1420, . . . , and 1430) may be selected as outputs using any ofthe conditions described above. After the final iteration, the output ofthe IC functional block 1430 is subtracted from the output of the delayelement Z^(−NM) 1493 whose delay is sufficient to match substantiallythe time required to perform the operations within each of the elementsof the IC functional blocks 1410, 1420, . . . , and 1430. This signal isde-spread using the despread functional block 1441 to generate softdecisions and then to a slicer 1442 to generate hard decisions therefrom; the de-spread functional block 1441 may be viewed as being anoutput de-spread functional block and the slicer 1442 may be viewed asbeing an output slicer.

[0099] The parallel implementation of the SIC functionality for CDMA1400 may be preferable in an application where hardware is notsignificantly limited by given design. Other designs, where hardware ismuch more constrained, or more expensive than hardware, may benefit froma serial implementation described below in FIG. 15.

[0100]FIG. 15 is a functional block diagram illustrating an embodimentof successive interference canceling (SIC) functionality for CDMA 1500that is arranged according to the invention in a serial implementation.In a block 1501, a spread signal is received from an element 1501 thathas undesirably introduced multipath interference. This multipathinterference may be caused by a variety of sources. For example, onesource of the multipath interference may be from the effects of thecommunication channel itself as shown in a block 1504. However, otherelements that may be employed to compensate for the existence ofnarrowband interference within a signal received by a communicationreceiver; sometimes, these introduced elements actually will introducesome degree of multipath interference. For example, some elements thatare employed to minimize the effects of ingress and/or narrowbandinterference may include an interference cancellation filter (ICF) 1502and/or an interference notch filter 1503. The multipath interferenceelement 1501 may be viewed, at the very least, as being an element thatintroduces multi-path effects into the signal received by the SICfunctionality for CDMA 1500. The attenuation of some of the componentenergy in the signals destroys the perfect orthogonality of the set ofCDMA symbols, which results in ICI. In general, the ICF suppresses or“notch filters” portions of the frequency domain, which is intended toattenuate ingress, but also introduces ICI in the process.

[0101] The FIG. 15 shows a functional block diagram of the serialimplementation of the invention. In this approach, a single successiveinterference canceling (SIC) stage is shown by an IC functional block1510. The IC functional block 1510 is implemented in such a way that itmay be used over and over again. The FIG. 15 shows an embodiment where asingle IC functional block is employed. Clearly, two IC functionalblocks could also be employed in a ping-pong embodiment as well.

[0102] For example, the signal output by the multipath interferenceelement 1501 is provided to the IC functional block 1510. The output ofthe IC functional block 1510 (after passing through only once) may beselected when there is no multipath interference in the received signalwhatsoever. The IC functional block 1510 includes a despread functionalblock 1511, a slicer 1512, a re-spread functional block 1513, and anICF-1 functional block 1514 (to perform convolution operations)according to the invention.

[0103] The despread functional block 1511 generates the soft decision ofthe received signal. The slicer 1512 makes a hard decision based on thesoft decision provided by the despread functional block 1511. These harddecisions by the slicer 1512 make the decisions offline with no cleaningof the signal; that is to say, without removing any ISI that existsamong the chips. These hard decisions may include a number of errorsthat would be too significant within data applications, but they willgive some accuracy of the received data even though there may be manyerror contained therein. This initial estimate of the data is thenre-spread, in the functional block 1513, to reconstruct the chip levelISI. Then, the operation within the ICF-1 functional block 1514generates the reconstructed ISI (on a chip level) of all of the othertaps besides this first tap.

[0104] This result (after passing through the IC functional block 1510one time) may then be provided to a memory management/processingfunctional block 1591. The original signal, received from the multipathinterference element 1501 has also been stored in a memory 1592 of thememory management/processing functional block 1591 where it has beenbuffered properly using delay elements 1593. The memorymanagement/processing functional block 1591 is also operable to transferand buffer subsequent interference cancelled versions of the signal aswell. Herein, the output from the IC functional block 1510 (afterpassing through one time) is subtracted from the buffered and delayedversion of the original signal using processing functionality 1594; thedelay length of the buffer would be Z-m that is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 1510. Multiple, and if desiredselectable, delay elements within the delay elements 1593 may be used toperform provide buffering and delaying of the various versions storedtherein. The memory management/processing functional block 1591 operatesin conjunction with the IC functional block 1510 to perform one, two, .. . , or more iterations of SIC functionality for CDMA using the ICfunctional block 1510 multiple times.

[0105] The memory management/processing functional block 1591 isoperable to perform buffering (of various sizes M, 2M, . . . , and(N−1)M, NM), which should be adequate to store the output of the ICFtill despread, slice, re-spread, and convolution operations are done insubsequent iterations. The ICF taps of the ICF-1 functional block 1514are chosen to notch out any present ingress in the signal in the variousiterations. The computation of these taps may be performed using anyapproach known in the art. This serial implementation of SICfunctionality for CDMA 1500 may be repeated successively if desired andmay be terminated using any of the criteria described within the FIG.14.

[0106] Clearly, the resultant will be cleaner for successive iterationsthat are performed using the serial implementation of SIC functionalityfor CDMA 1500, as it will for performing multiple stages of the parallelimplementation of SIC functionality for CDMA 1400. After the finaliteration that is performed, the signal is passed to a despreadfunctional block 1521 and to a slicer 1522 to generate the final outputsignal.

[0107] Alternatively, after the final iteration that is performed, thesignal is passed to the despread functional block 1511 and to the slicer1512 to generate the final output signal; this way the hardware withinthe IC functional block 1510 may be put to maximum use, and the despreadfunctional block 1521 and the slicer 1522 would not be needed at all.Each of the despread functional block 1511 and 1521 may be viewed asbeing an output de-spread functional block, and each of the slicer 1512and 1522 may be viewed as being an output slicer. It is also noted thata combination embodiment may include a portion of the parallelimplementation of the FIG. 14 and a portion of the serial implementationof the FIG. 15 without departing from the scope and spirit of theinvention.

[0108] The various embodiments described above within the FIGS. 14 and15 may be viewed as those that are operable to deal with systems thatare fully synchronized, in that, the received symbols are not undergoingany rotation at all. That is to say, these embodiments are operable tosupport SIC functionality for CDMA when no rotation correction and/orcompensation needs to be performed. The potentially disastrous effectsof rotation of received symbols is described using a nominal 30 degreerotation within a variety of constellation types employed within variousmodulations. As will be seen, rotation of the constellation's of lowerorder modulations may sometimes even be tolerated. However, as thenumber of constellation points of the higher order modulations continuesto increase, then the fragility of the modulation becomes such that evenrelatively small amounts of rotation can prove disastrous when trying tomake soft and hard decisions.

[0109]FIG. 16 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of QPSK (Quadrature Phase ShiftKeying) modulation. On the left hand side, 4 constellation points of aQPSK modulation are shown as being aligned at 90 degree intervals withrespect to the I,Q axes. On the right hand side, the 4 constellationpoints are shown after having undergone a nominal 30 degree rotation. Ascan been seen in this example, the constellation points still residewithin their original quadrant. Within the QPSK modulation, given thatonly one constellation point is contained within each quadrant, thenthis particular modulation may accommodate relatively small degrees ofrotation.

[0110]FIG. 17 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of 8 PSK (8 Phase Shift Keying)modulation. On the left hand side, 8 constellation points of an 8 PSKmodulation are shown as being aligned at 45 degree intervals withrespect to the I,Q axes. On the right hand side, the 8 constellationpoints are shown after having undergone a nominal 30 degree rotation. Ascan been seen in this example, some of the constellation points nolonger reside within their original quadrant. Perhaps more problematicis the fact that some of the constellation points now nearly overlapwith the positions of where other constellation points are expected tobe located. In this situation, even a relatively small degree ofrotation can be extremely problematic.

[0111] As the number of constellation points employed within themodulation continues to increase, the problems introduced by rotationcontinue to be exacerbated.

[0112]FIG. 18 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of 16 QAM (Quadrature AmplitudeModulation) modulation. On the left hand side, 16 constellation pointsof a 16 QAM modulation are shown as being aligned with respect to theI,Q axes. On the right hand side, the 16 constellation points are shownafter having undergone a nominal 30 degree rotation. As can been seen inthis example, some of the constellation points no longer reside withintheir original quadrant. Perhaps more problematic is the fact thatseveral of the constellation points almost overlap with the positions ofwhere other constellation points are expected to be located. Given thatthere are 16 constellation points involved, the negative effectsintroduced by the rotation are extreme. In this situation, even arelatively small degree of rotation is extremely problematic.

[0113]FIG. 19 is a diagram illustrating the effects of rotation onsymbols coded using a constellation of 16 APSK (Amplitude Phase ShiftKeying) modulation. On the left hand side, 16 constellation points of a16 APSK modulation are shown as being aligned with respect to the I,Qaxes. On the right hand side, the 16 constellation points are shownafter having undergone a nominal 30 degree rotation. Again, as can beenseen in this example, some of the constellation points no longer residewithin their original quadrant. Similar to the 16 QAM example, perhapsmore problematic is the fact that several of the constellation pointsalmost overlap with the positions of where other constellation pointsare expected to be located. Also similar to the 16 QAM example, giventhat there are 16 constellation points involved, the negative effectsintroduced by the rotation are extreme. In this situation, even arelatively small degree of rotation is extremely problematic.

[0114] It is also understood that even higher order modulations willsuffer even more greatly from the effects of rotation. For example, thedegradation of performance of constellation points of a 256 QAM or 1024QAM modulation could be even greater given that even more constellationpoints may nearly overlap and interfere with one another. Performingaccurate soft and hard decisions will be virtually impossible.

[0115]FIG. 20 is a functional block diagram illustrating an embodimentof successive interference canceling (SIC) functionality for CDMA thatis arranged according to the invention in a parallel implementation thatis operable to compensate for rotation. In a block 2001, a spread signalis received from an element 2001 that has undesirably introducedmultipath interference. This multipath interference may be caused by avariety of sources. For example, one source of the multipathinterference may be from the effects of the communication channel itselfas shown in a block 2004. However, other elements that may be employedto compensate for the existence of narrowband interference within asignal received by a communication receiver; sometimes, these introducedelements actually will introduce some degree of multipath interference.For example, some elements that are employed to minimize the effects ofingress and/or narrowband interference may include an interferencecancellation filter (ICF) 2002 and/or an interference notch filter 2003.The multipath interference element 2001 may be viewed, at the veryleast, as being an element that introduces multi-path effects into thesignal received by the SIC functionality for CDMA 2000. The attenuationof some of the component energy in the signals destroys the perfectorthogonality of the set of CDMA symbols, which results in ICI. Ingeneral, the ICF suppresses or “notch filters” portions of the frequencydomain, which is intended to attenuate ingress, but also introduces ICIin the process.

[0116] The FIG. 20 shows a functional block diagram of the parallelimplementation of the invention that is operable to compensate forrotation. In this approach, two or more successive interferencecanceling (SIC) stages are shown by the IC functional blocks, and eachof those IC functional blocks is operable to compensate for rotation ofthe symbols within the received signal. The approach also employs abuffer of size M, which should be adequate to store the output of theICF till despread, derotate, slice, rerotate, re-spread, and convolutionoperations are done. The ICF taps are chosen to notch out (or “blank”)any present ingress in the signal. The computation of these taps may beperformed using any approach known in the art.

[0117] For example, the signal output by the multipath interferenceelement 2001 is simultaneously provided to an interference cancellation(IC) functional block 2010 and a delay element Z^(−M) 2091. Whenmultiple iterations of ICF are to performed using the SIC functionalityfor CDMA 2000, . . . the output of the multipath interference element2001 is also simultaneously provided to a delay element Z^(−(N−1)M) 2092(when multiple iterations are performed), and to a delay element Z^(−NM)2092 (when N iterations are performed). The output of the IC functionalblock 2010 may be selected when there is no multipath interference inthe received signal whatsoever. The IC functional block 2010 includes adespread functional block 2011, a slicer 2012, a re-spread functionalblock 2013, and an ICF-1 functional block 2014 (to perform convolutionoperations) according to the invention.; the ICF-1 functional blocksdescribed herein may also be referred to as convolution functionalblocks.

[0118] The despread functional block 2011 generates the soft decision ofthe received signal. The output of the despread functional block 2011 issimultaneously passed to a parameter estimator 2019 and a derotator2016. The parameter estimator 2019 may employ preamble processingthereby using known and expected symbols to perform the rotationestimation of the received signal. Alternatively, the parameterestimator 2019 may also employ a portion of the payload (or data) of areceived data segment as well. Once an actual estimation of the rotationis made, then the parameter estimator provides this rotation estimate tothe derotator 2016. The derotator 2016 may include a buffer that matchesthe time period in which the parameter estimator 2019 takes to performits estimation of the rotation within the signal. In addition, theparameter estimator provides this rotation estimate to the rerotator2018 that is operable to add the rotation back into the signal, afterslicing has been performed by the slicer 2012, for subsequent iterationsof the SIC functionality for CDMA.

[0119] The slicer 2012 makes a hard decision based on the soft decisionprovided by the despread functional block 2011. These hard decisions bythe slicer 2012 make the decisions offline with no cleaning of thesignal; that is to say, without removing any ISI that exists among thechips. These hard decisions may include a number of errors that would betoo significant within data applications, but they will give someaccuracy of the received data even though there may be many errorcontained therein.

[0120] This initial estimate of the data is then passed to the rerotator2018 and then this result is re-spread, in the functional block 2013, toreconstruct the chip level ISI. Then, the operation within the ICF-1functional block 2014 generates the reconstructed ISI (on a chip level)of all of the other taps besides this first tap. This result may then besubtracted from the output of the delay element Z^(−M) 2091. The delaylength of the buffer, delay element Z^(−M) 2091, is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 2010.

[0121] This chain of IC functionality, including parameter estimationdirected derotation and rerotation, may be repeated successively ifdesired to provide for even further improved performance. For example,the output of the node (the first summing node) where the output of thedelay element Z^(−M) 2091 and the negative output of the IC functionalblock 2010 are summed together may be fed into an IC functional block2020. The IC functional block 2020 will include comparable elements ofthe IC functional block 2010. For example, the IC functional block 2020includes a despread functional block 2021 that generates soft decisionof the output from the first summing node. Similarly, a parameterestimator 2029, a derotator 2026, and a rerotator 2028 all operate, insimilar manner to the parameter estimator 2019, the derotator 2016, andthe rerotator 2018 of the IC functional block 2010, to compensate forany rotation within the signal at this point within the processing.

[0122] After the signal passes through the derotator 2026, a slicer 2022makes a hard decision based on the soft decision provided by thedespread functional block 2021. These hard decisions by the slicer 2022make the decisions offline with an improved, cleaner signal; that is tosay, some of the ISI that exists among the chips will have been removedby the operations described above. These hard decisions will include afewer number of errors than in the previous chain of IC functionality.

[0123] This next 2^(nd) order initial estimate of the data is thenpassed to the rerotator 2028 and then this result is then re-spread, ina functional block 2023, to reconstruct the chip level ISI (which willbe reduced when compared to the previous chain).

[0124] Then, the operation within a ICF-1 functional block 2024generates the reconstructed ISI (on a chip level) of all of the othertaps besides this first tap; again, this reconstructed ISI will berelatively less than in the first chain. This result may then besubtracted from the output of a delay element Z^(−(N−1)M) 2092. Thedelay length of the buffer, delay element Z^(−(N−1)M) 2092, issufficient to match substantially the time required to perform theoperations within each of the elements of the IC functional block 2010,within each of the elements of the IC functional block 2020, and anyadditional IC functional blocks that are employed.

[0125] It is noted that the resultant output of the slicer 2012 withinthe IC functional block 2010 may be selected as an output.Alternatively, the resultant output of the slicer 2022 within the ICfunctional block 2020 may be selected as an output when it has beendetermined that a solution has been reached (say when a differencebetween potential output 0 and potential output 1 are within apredetermined degree of magnitude). Alternatively, this potential output1 may be selected when a predetermined number of chains (2 in such anembodiment) are selected to be performed. Another method of determiningwhen to end this process is to look at the Signal to Noise Ratio (SNR)of the signal and to select the output from one of the stages when theSNR meets a predetermined threshold.

[0126] Subsequent chains may be implemented successively as desired toprovide even further performance. For example, multiple chains may beincluded up to perform even additional SIC functionality for CDMAaccording to the invention.

[0127] After the final iteration, the output of the IC functional block2020 is subtracted from the output of the delay element Z^(−NM) 2093whose delay is sufficient to match substantially the time required toperform the operations within each of the elements of the IC functionalblocks 2010, 2020, . . . , and any other IC functional blocks. Thissignal is de-spread using the despread functional block 2041 to generatesoft decisions. This result is then passed simultaneously to a parameterestimator 2049 and a derotator 2046. The output from the derotator 2046is then passed to a slicer 2042 to generate hard decisions there from;the despread functional block 2041, along with the parameter estimator2049 and the derotator 2046, may be viewed as being the outputprocessing functional blocks associated with the slicer 2042 to generatean output, namely, the potential output N.

[0128] The parallel implementation of the SIC functionality for CDMA2000 may be preferable in an application where hardware is notsignificantly limited by given design and compensating for rotation inthe received signal is a design criteria or consideration. Otherdesigns, where hardware is much more constrained, or more expensive thanhardware, may benefit from a serial implementation described below inFIG. 21 that is also operable to perform derotation and rerotation.

[0129]FIG. 21 is a functional block diagram illustrating an embodimentof SIC functionality for CDMA that is arranged according to theinvention in a serial implementation that is operable to compensate forrotation. In a block 2101, a spread signal is received from an element2101 that has undesirably introduced multipath interference. Thismultipath interference may be caused by a variety of sources. Forexample, one source of the multipath interference may be from theeffects of the communication channel itself as shown in a block 2104.However, other elements that may be employed to compensate for theexistence of narrowband interference within a signal received by acommunication receiver; sometimes, these introduced elements actuallywill introduce some degree of multipath interference. For example, someelements that are employed to minimize the effects of ingress and/ornarrowband interference may include an interference cancellation filter(ICF) 2102 and/or an interference notch filter 2103. The multipathinterference element 2101 may be viewed, at the very least, as being anelement that introduces multi-path effects into the signal received bythe SIC functionality for CDMA 2100. The attenuation of some of thecomponent energy in the signals destroys the perfect orthogonality ofthe set of CDMA symbols, which results in ICI. In general, the ICFsuppresses or “notch filters” portions of the frequency domain, which isintended to attenuate ingress, but also introduces ICI in the process.

[0130] The FIG. 21 shows a functional block diagram of the serialimplementation of the invention that is operable to compensate forrotation. In this approach, a single successive interference canceling(SIC) stage is shown by an IC functional block 2110. The IC functionalblock 2110 is implemented in such a way that it may be used over andover again. The FIG. 21 shows an embodiment where a single IC functionalblock is employed. Clearly, two IC functional blocks could also beemployed in a ping-pong embodiment as well without departing from thescope and spirit of the invention.

[0131] For example, the signal output by the multipath interferenceelement 2101 is provided to the IC functional block 2110. The output ofthe IC functional block 2110 (after passing through only once) may beselected when there is no multipath interference in the received signalwhatsoever. The IC functional block 2110 includes a despread functionalblock 2111, a parameter estimator 2119, a derotator 2116, a slicer 2112,a rerotator 2118, a re-spread functional block 2113, and an ICF-1functional block 2114 (to perform convolution operations) according tothe invention. The elements within the IC functional block 2110 operatecooperatively in a similar fashion to the IC functional blocks withinthe FIG. 20.

[0132] The despread functional block 2111 generates the soft decision ofthe received signal. The output of the despread functional block 2111 issimultaneously provided to the parameter estimator 2119 and thederotator 2116. The slicer 2112 makes a hard decision based on the softdecision provided by the derotator 2116 after having passed through thedespread functional block 2111. These hard decisions by the slicer 2112may be made offline with no cleaning of the signal; that is to say,without removing any ISI that exists among the chips. These harddecisions may include a number of errors that would be too significantwithin data applications, but they will give some accuracy of thereceived data even though there may be many error contained therein.This initial estimate of the data is passed to the rerotator 2118 andthen this result is then re-spread, in the functional block 2113, toreconstruct the chip level ISI. Then, the operation within the ICF-1functional block 2114 generates the reconstructed ISI (on a chip level)of all of the other taps besides this first tap.

[0133] This result (after passing through the IC functional block 2110one time) may then be provided to a memory management/processingfunctional block 2191. The original signal, received from the multipathinterference element 2101 has also been stored in a memory 2192 of thememory management/processing functional block 2191 where it has beenbuffered properly using delay elements 2193. The memorymanagement/processing functional block 2191 is also operable to transferand buffer subsequent interference cancelled versions of the signal aswell. Herein, the output from the IC functional block 2110 (afterpassing through one time) is subtracted from the buffered and delayedversion of the original signal using processing functionality 2194; thedelay length of the buffer would be Z-M that is sufficient to matchsubstantially the time required to perform the operations within each ofthe elements of the IC functional block 2110. Multiple, and if desiredselectable, delay elements within the delay elements 2193 may be used toperform provide buffering and delaying of the various versions storedtherein. The memory management/processing functional block 2191 operatesin conjunction with the IC functional block 2110 to perform one, two, .. . , or more iterations of SIC functionality for CDMA using the ICfunctional block 2110 multiple times.

[0134] The memory management/processing functional block 2191 isoperable to perform buffering (of various sizes M, 2M, . . . , and(N−1)M, NM), which should be adequate to store the output of the ICFtill despread, derotated, slice, rerotated, re-spread, and convolutionoperations are done in subsequent iterations. The ICF taps of the ICF-1functional block 2114 are chosen to notch out any present ingress in thesignal in the various iterations. The computation of these taps may beperformed using any approach known in the art. This serialimplementation of SIC functionality for CDMA 2100 may be repeatedsuccessively if desired and may be terminated using any of the criteriadescribed within the FIG. 20.

[0135] Clearly, the resultant will be cleaner for successive iterationsthat are performed using the serial implementation of SIC functionalityfor CDMA 2100, as it will for performing multiple stages of the parallelimplementation of SIC functionality for CDMA 2000 that is also operableto correct for rotation. After the final iteration that is performed,the signal is passed to a despread functional block 2121, to a parameterestimator 2129 and a derotator 2126, and then to a slicer 2122 togenerate the final output signal.

[0136] Alternatively, after the final iteration that is performed, thesignal is passed to the despread functional block 2111, to the derotator2116, and to the slicer 2112 to generate the final output signal; thisway the hardware within the IC functional block 2110 may be put tomaximum use, and the despread functional block 2121 and the slicer 2122would not be needed at all. Each of the de-spread functional block2111/derotator 2116 and the de-spread functional block 2121/derotator2126 may be viewed as being the output functional blocks that operatecooperatively with the slicers 2112 and 2122 to generate the finalpotential outputs. It is also noted that a combination embodiment mayinclude a portion of the parallel implementation of the FIG. 20 and aportion of the serial implementation of the FIG. 21 without departingfrom the scope and spirit of the invention.

[0137] The various embodiments described above within the FIGS. 20 and21 may be viewed as those that are operable to deal with systems thatare not fully synchronized, in that, the received symbols may actuallyhave undergone some rotation. That is to say, these embodiments areoperable to support SIC functionality for CDMA when rotation correctionand/or compensation may need to be performed.

[0138]FIG. 22 is an operational flow diagram illustrating an embodimentof an SIC method for CDMA 2200 that is performed according to theinvention. In a block 2210, a signal is received that has some degree ofinterference contained therein. In a block 2220, the signal is despreadand soft decisions are made of the despread signal. These soft decisionsare sliced as shown in a block 2230 thereby generating hard decisions.Clearly, some of these hard decisions may include some errors, giventhat no SIC functionality for CDMA has yet to be made on the signal.Then, in a block 2240, these hard decisions are re-spread. The ICF tapsof an ICF are chosen in a block 2250, using any manner known in the art,that will subsequently be used to convolve the hard decisions (allexcept the first tap) as shown in a block 2260. This convolved signal,output of an ICF-1 functional block, is then subtracted from thebuffered and delayed version of the original signal as shown in a block2270.

[0139] This process may be performed successively. The SIC method forCDMA 2200 may terminate when it has been determined that a solution hasbeen reached (say when a difference between one iteration and asubsequent iteration are within a predetermined degree of magnitude).Alternatively, a predetermined number of iterations may be performed inevery case (this number of iterations may be selectable andprogrammable). Another method of determining when to end this process isto look at the Signal to Noise Ratio (SNR) of the signal and to selectthe output from one of the stages when the SNR meets a predeterminedthreshold.

[0140] After the total number of iterations has been performed accordingto the FIG. 24, the final output signal is then de-spread therebygenerating soft decisions and sliced to generate the final output harddecisions. This may be performed using any of the various embodimentsdescribed herein.

[0141]FIG. 23 is an operational flow diagram illustrating anotherembodiment of an SIC method for CDMA 2300 that is performed according tothe invention. In a block 2310, a signal is received that has somedegree of interference contained therein. In a block 2220, the signal isdespread and soft decisions are made of the despread signal. In a block2322, parameter estimation is made on this signal in an effort toestimate the rotation of the symbols within the received signal. Thismay be performed using preamble processing in certain embodiments.Alternatively, this may be performed using a portion of the payload (ordata) of a received data segment as well. After the estimate of therotation is made, then any rotation within the signal is then derotatedas shown in a block 2324. Then, this result then undergoes slicing asshown in a block 2230 thereby generating hard decisions. In someembodiments, the signal at this point is taken as the final outputsignal. However, it is noted that some of these hard decisions mayinclude some errors, given that no SIC functionality for CDMA has yet tobe made on the signal. However, within embodiments that do not take thesignal at this point as the final output and where multiple iterationsare performed, any rotation that has been derotated is then rerotatedback into the signal at this point as shown in a block 2332.

[0142] Then, in a block 2340, these hard decisions, that do include anyrotation having been rerotated back in, are re-spread. The ICF taps ofan ICF are chosen in a block 2350, using any manner known in the art,that will subsequently be used to convolve the hard decisions (allexcept the first tap) as shown in a block 2360. This convolved signal,output of an ICF-1 functional block, is then subtracted from thebuffered and delayed version of the original signal as shown in a block2370.

[0143] This process may be performed successively. The SIC method forCDMA 2300 may terminate when it has been determined that a solution hasbeen reached (say when a difference between one iteration and asubsequent iteration are within a predetermined degree of magnitude).Alternatively, a predetermined number of iterations may be performed inevery case (this number of iterations may be selectable andprogrammable). Another method of determining when to end this process isto look at the Signal to Noise Ratio (SNR) of the signal and to selectthe output from one of the stages when the SNR meets a predeterminedthreshold.

[0144] After the total number of iterations has been performed accordingto the FIG. 23, the final output signal is then de-spread therebygenerating soft decisions and sliced to generate the final output harddecisions. This may be performed using any of the various embodimentsdescribed herein.

[0145]FIG. 24 is a diagram illustrating a number of considerations ofwhich iteration(s) to perform rotation correction according to theinvention. One determination may be made based on the type of modulationthat is employed. For example, those modulations that employ fewernumbers of constellation points may not need as much rotationcorrection, if any at all, as those that employ higher numbers ofconstellation points.

[0146] Another consideration may be based on what processing type isemployed to perform rotation estimation. For example, some embodimentsmay employ preamble processing that employs only the preamble symbols ofa received signal. Other embodiments may employ both the preamble andany payload as well. There may be a system may not include sufficientprocessing resources to perform preamble and payload processing everytime. Within some iterations, the system may perform rotationcorrection, but it may not in all of the iterations.

[0147] Yet another consideration may be based on a predetermined orderof which iterations should undergo rotation correction. For example,some embodiments perform rotation correction at every iterationincluding the beginning, the middle, and the end. Other embodiments willperform rotation correction only at the beginning, or only at the end.

[0148] Yet another consideration is the magnitude of the rotation error.When the magnitude exceeds a particular threshold, then the rotationcorrection may be performed according to the invention. When themagnitude does not exceed that particular threshold, then the rotationcorrection need not be performed according to the invention. Inaddition, the consideration may be adaptive in nature. This may involveconsidering either one or both of the system operating conditions andthe availability of processing resources that may be capable to performthe rotation correction.

[0149]FIG. 25 shows an embodiment of SIC for CDMA simulation resultsaccording to the invention. The FIG. 25 show simulation results fordespreader output constellations of three SIC iterations in an SCDMAsystem with 120 active codes and QPSK (Quadrature Phase Shift Keying)modulation, which uses an ICF whose tap magnitudes are shown in theupper right hand side of FIG. 25. The lower right hand side of FIG. 25shows the hard decision SER versus the SIC iteration (i=0, for no SIC,and when i=1, 2, 3, 4, and 5). The FIG. 25 show that the SIC procedureaccording to the invention converges, in this case, in 3 iterations.Again, the number of iterations to be performed may be selectedappropriately for the given situation. The number of iterations may bepredetermined, it may be determined based upon convergence of theconstellation points, and/or it may be determined by looking at somemeasurand such as SNR in the received signal after having undergonevarious iterations of SIC for CDMA.

[0150] In view of the above detailed description of the invention andassociated drawings, other modifications and variations will now becomeapparent. It should also be apparent that such other modifications andvariations may be effected without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A communication receiver that is operable tocancel inter-code-interference within a signal, comprising: aninterference cancellation functional block that de-spreads, slices,re-spreads, and convolves the signal using a selected plurality ofinterference cancellation filter taps thereby generating a convolvedsignal; a delay element that receives the signal and delays the signalfor a period of time substantially matching a time the signal isprocessed within the interference cancellation functional block; whereinthe communication receiver subtracts the convolved signal from a delayedoutput signal that is provided from the delay element thereby generatinga cleaned signal; and an output de-spread functional block thatgenerates a plurality of output soft decisions from the cleaned signal;and an output slicer that generates a plurality of output hard decisionsusing the plurality of output soft decisions.
 2. The communicationreceiver of claim 1, further comprising at least one additionalinterference cancellation functional block that de-spreads, slices,re-spreads, and convolves the cleaned signal using a selected pluralityof interference cancellation filter taps thereby generating at least oneadditional convolved signal; wherein the communication receiversubtracts the at least one additional convolved signal from a delayedoutput signal that is provided from at least one additional delayelement thereby generating at least one additional cleaned signal; andthe output de-spread functional block generates at least one additionalplurality of output soft decisions from the at least one additionalcleaned signal; the output slicer generates at least one additionalplurality of output hard decisions using the at least one additionalplurality of output soft decisions; and the interference cancellationfunctional block and the at least one additional interferencecancellation functional block are arranged within a parallelimplementation.
 3. The communication receiver of claim 2, wherein thecommunication receiver compares a difference between the plurality ofoutput hard decisions and the at least one additional plurality ofoutput hard decisions with a predetermined threshold; and thecommunication receiver selects the plurality of output hard decisionswhen the predetermined threshold exceeds the difference.
 4. Thecommunication receiver of claim 1, further comprising a memorymanagement/processing functional block, comprising memory and delayelements, that is operable to perform transfer and buffering of thesignal and interference cancelled versions of the signal; and the memorymanagement/processing functional block and the interference cancellationfunctional block operate cooperatively to perform successiveinterference cancellation of the inter-code-interference within thesignal.
 5. The communication receiver of claim 1, wherein the inter-codeinterference comprises multi-path interference introduced by acommunication channel over which the signal has been communicated to thecommunication receiver.
 6. The communication receiver of claim 1,wherein the inter-code interference comprises is generated by at leastone of an interference cancellation filter within the communicationreceiver and an interference notch filter within the communicationreceiver that is implemented to compensate for narrowband within thesignal that has been communicated to the communication receiver.
 7. Thecommunication receiver of claim 1, wherein the communication receivercomprises at least one of a multi-channel headend physical layer burstreceiver, a base station receiver, a mobile receiver, a satellite earthstation, a tower receiver, a high definition television set top boxreceiver, and a Bluetooth™ operable device.
 8. The communicationreceiver of claim 1, wherein the interference cancellation functionalblock further comprises: a parameter estimator that receives theplurality of output soft decisions from the cleaned signal, generated bythe output de-spread functional block, and generates an estimate ofrotation contained therein; and a derotator that is operable to derotatethe plurality of output soft decisions according to the estimate ofrotation before providing the plurality of output soft decisions to theoutput slicer.
 9. The communication receiver of claim 8, wherein theinterference cancellation functional block further comprises: arerotator that is operable to rerotate the plurality of output harddecisions that are generated by the slicer; and a re-spread functionalblock that re-spreads the plurality of output hard decisions.
 10. Thecommunication receiver of claim 1, wherein the communication receivercomprises a headend physical layer burst receiver.
 11. The communicationreceiver of claim 10, wherein the headend physical layer burst receiveris communicatively coupled to a cable modem termination system mediumaccess controller.
 12. The communication receiver of claim 1, whereinthe communication receiver is contained within at least one of a cablemodem termination system and a transceiver.
 13. A communication receiverthat is operable to cancel inter-code-interference within a signal thatis coded using code division multiple access, comprising: aninterference cancellation functional block, comprising a despreadfunctional block, a slicer, a re-spread functional block, and aconvolutional functional block, that receives the signal; and a delayelement that also receives the signal and delays the signal for a periodof time substantially matching a time the signal is processed within theinterference cancellation functional block; and wherein the de-spreadfunctional block generates a plurality of soft decisions from thesignal; the slicer generates a plurality of hard decisions using theplurality of soft decisions, the plurality of hard decisions comprisingcorrect hard decisions and error hard decisions; the re-spreadfunctional block re-spreads the plurality of hard decisions to generatea re-spread signal; the convolutional functional block, comprising aplurality of taps that are operable to compensate for theinter-code-interference interference, convolves the re-spread signalwith at least one additional plurality of taps to generate a convolvedsignal, the at least one additional plurality of taps includes all ofthe taps within the plurality of taps except a first tap; thecommunication receiver subtracts the convolved signal from a delayedoutput signal that is provided from the delay element thereby generatinga cleaned signal; and an output de-spread functional block thatgenerates a plurality of output soft decisions from the cleaned signal;and an output slicer that generates a plurality of output hard decisionsusing the plurality of output soft decisions, the plurality of outputhard decisions comprising fewer error hard decisions than the pluralityof hard decisions.
 14. The communication receiver of claim 13, whereinthe inter-code interference comprises multi-path interference introducedby a communication channel over which the signal has been communicatedto the communication receiver.
 15. The communication receiver of claim13, wherein the inter-code interference comprises is generated by atleast one of an interference cancellation filter within thecommunication receiver and an interference notch filter within thecommunication receiver that is implemented to compensate for narrowbandwithin the signal that has been communicated to the communicationreceiver.
 16. The communication receiver of claim 13, further comprisinga memory management/processing functional block, comprising memory anddelay elements, that is operable to perform transfer and buffering ofthe signal and interference cancelled versions of the signal; and thememory management/processing functional block and the interferencecancellation functional block operate cooperatively to performsuccessive interference cancellation of the inter-code-interferencewithin the signal.
 17. The communication receiver of claim 13, whereinthe communication receiver selectively performs additional iterations ofsuccessive interference cancellation of the intercode-interference whena signal to noise ratio of the plurality of output hard decisionsexceeds a predetermined threshold.
 18. The communication receiver ofclaim 13, wherein the communication receiver selectively performs apredetermined number of iterations of successive interferencecancellation of the inter-code-interference within the signal.
 19. Thecommunication receiver of claim 13, wherein the interferencecancellation functional block further comprises: a parameter estimatorthat receives the plurality of soft decisions from the signal, generatedby the de-spread functional block, and generates an estimate of rotationcontained therein; and a derotator that is operable to derotate theplurality of soft decisions according to the estimate of rotation beforeproviding the plurality of soft decisions to the slicer.
 20. Thecommunication receiver of claim 19, wherein the interferencecancellation functional block further comprises: a rerotator that isoperable to rerotate the plurality of output hard decisions that aregenerated by the slicer; and a re-spread functional block thatre-spreads the plurality of output hard decisions.
 21. The communicationreceiver of claim 13, further comprising: a parameter estimator thatreceives the plurality of output soft decisions from the cleaned signal,generated by the output de-spread functional block, and generates anestimate of rotation contained therein; and a derotator that is operableto derotate the plurality of output soft decisions according to theestimate of rotation before providing the plurality of output softdecisions to the output slicer.
 22. The communication receiver of claim13, wherein the communication receiver comprises at least one of amulti-channel headend physical layer burst receiver, a base stationreceiver, a mobile receiver, a satellite earth station, a towerreceiver, a high definition television set top box receiver, and aBluetooth™ operable device.
 23. The communication receiver of claim 13,wherein the communication receiver comprises a headend physical layerburst receiver.
 24. The communication receiver of claim 23, wherein theheadend physical layer burst receiver is communicatively coupled to acable modem termination system medium access controller.
 25. Thecommunication receiver of claim 13, wherein the communication receiveris contained within at least one of a cable modem termination system anda transceiver.
 26. A communication receiver that is operable to cancelinter-code-interference within a signal that is coded using codedivision multiple access, comprising: a plurality of interferencecancellation functional blocks arranged in a parallel implementation; aplurality of delay elements, that precede a second interferencecancellation functional block and any subsequent interferencecancellation functional blocks within the plurality of interferencecancellation functional blocks, that are each operable to delay thesignal for a period of time substantially matching an integer multipleof a time the signal is processed within one of the interferencecancellation functional blocks; and wherein each interferencecancellation functional block, within the plurality of interferencecancellation functional blocks, comprises a despread functional block, aslicer, a re-spread functional block, and a convolutional functionalblock; a first de-spread functional block generates a first plurality ofsoft decisions from the signal; a first slicer generates a plurality offirst hard decisions using the first plurality of soft decisions, thefirst plurality of hard decisions comprising correct hard decisions anderror hard decisions; a first re-spread functional block re-spreads thefirst plurality of hard decisions to generate a first re-spread signal;a first convolutional functional block, comprising a plurality of tapsthat are operable to compensate for the inter-code-interferenceinterference, that convolves the first re-spread signal with at leastone additional plurality of taps to generate a first convolved signal,the at least one additional plurality of taps includes all of the tapswithin the plurality of taps except a first tap; the communicationreceiver subtracts the first convolved signal from a delayed outputsignal from a first delay element thereby generating a first cleanedsignal, the first delay element is operable to delay the signal for aperiod of time substantially matching the time the signal is processedwithin one of the interference cancellation functional blocks; a secondde-spread functional block generates a second plurality of softdecisions from the first cleaned signal; a second slicer generates aplurality of second hard decisions using the second plurality of softdecisions, the second plurality of hard decisions comprising morecorrect hard decisions and fewer error hard decisions that the firstplurality of hard decisions; a second re-spread functional blockre-spreads the second plurality of hard decisions to generate a secondre-spread signal; a second convolutional functional block that convolvesthe second re-spread signal with the at least one additional pluralityof taps to generate a second convolved signal; the communicationreceiver subtracts the second convolved signal from a delayed outputsignal from a second delay element thereby generating a second cleanedsignal, the second delay element is operable to delay the signal for aperiod of time substantially matching twice the time the signal isprocessed within one of the interference cancellation functional blocks;and an output de-spread functional block that generates a plurality ofoutput soft decisions from the second cleaned signal; and an outputslicer that generates a plurality of output hard decisions using theplurality of output soft decisions, the plurality of output harddecisions comprising fewer error hard decisions than the secondplurality of hard decisions.
 27. The communication receiver of claim 26,wherein the inter-code interference comprises multi-path interferenceintroduced by a communication channel over which the signal has beencommunicated to the communication receiver.
 28. The communicationreceiver of claim 26, wherein the inter-code interference comprises isgenerated by at least one of an interference cancellation filter withinthe communication receiver and an interference notch filter within thecommunication receiver that is implemented to compensate for narrowbandwithin the signal that has been communicated to the communicationreceiver.
 29. The communication receiver of claim 26, further comprisinga memory management/processing functional block, comprising memory anddelay elements, that is operable to perform transfer and buffering ofthe signal and interference cancelled versions of the signal; and thememory management/processing functional block and at least one of thefirst interference cancellation functional block and the secondinterference cancellation functional block operate cooperatively toperform successive interference cancellation of theinter-code-interference within the signal.
 30. The communicationreceiver of claim 26, wherein the communication receiver selectivelyperforms additional iterations of successive interference cancellationof the intercode-interference when a signal to noise ratio of theplurality of output hard decisions exceeds a predetermined threshold.31. The communication receiver of claim 26, wherein the communicationreceiver selectively performs a predetermined number of iterations ofsuccessive interference cancellation of the inter-code-interferencewithin the signal.
 32. The communication receiver of claim 26, wherein afirst interference cancellation functional block within the plurality ofinterference cancellation functional blocks further comprises: aparameter estimator that receives the first plurality of soft decisionsfrom the signal, generated by the first de-spread functional block, andgenerates an estimate of rotation contained therein; and a derotatorthat is operable to derotate the first plurality of soft decisionsaccording to the estimate of rotation before providing the firstplurality of soft decisions to the first slicer.
 33. The communicationreceiver of claim 32, wherein the first interference cancellationfunctional block within the plurality of interference cancellationfunctional blocks further comprises: a rerotator that is operable torerotate the first plurality of output hard decisions that are generatedby the first slicer before providing the first plurality of output harddecisions to the first re-spread functional block.
 34. The communicationreceiver of claim 26, further comprising: a parameter estimator thatreceives the plurality of output soft decisions from the second cleanedsignal, generated by the output de-spread functional block, andgenerates an estimate of rotation contained therein; and a derotatorthat is operable to derotate the plurality of output soft decisionsaccording to the estimate of rotation before providing the plurality ofoutput hard decisions comprising fewer error hard decisions than thesecond plurality of hard decisions to the output slicer.
 35. Thecommunication receiver of claim 26, wherein the communication receivercomprises at least one of a multi-channel headend physical layer burstreceiver, a base station receiver, a mobile receiver, a satellite earthstation, a tower receiver, a high definition television set top boxreceiver, and a Bluetooth™ operable device.
 36. The communicationreceiver of claim 26, wherein the communication receiver comprises aheadend physical layer burst receiver.
 37. The communication receiver ofclaim 36, wherein the headend physical layer burst receiver iscommunicatively coupled to a cable modem termination system mediumaccess controller.
 38. The communication receiver of claim 26, whereinthe communication receiver is contained within at least one of a cablemodem termination system and a transceiver.
 39. A successiveinterference canceling method for code division multiple access, themethod comprising: despreading a signal that comprisesinter-code-interference thereby making a plurality of soft decisions;slicing the plurality of soft decisions thereby making a plurality ofhard decisions; re-spreading the plurality of hard decisions; convolvingthe hard decisions with a selected plurality of interferencecancellation filter taps thereby generating a convolved signal, theselected plurality of interference cancellation filter taps beingcomprising a plurality of interference cancellation filter taps thatexcludes a first filter tap; and subtracting the convolved signal with adelayed version of the signal to generate a cleaned signal.
 40. Themethod of claim 39, further comprising: despreading the cleaned signalthereby making a plurality of output soft decisions; and slicing theplurality of output soft decisions thereby making a plurality of outputhard decisions.
 41. The method of claim 39, further comprising:despreading the cleaned signal thereby making at least one additionalplurality of soft decisions; slicing the at least one additionalplurality of soft decisions thereby making at least one additionalplurality of hard decisions; re-spreading the at least one additionalplurality of hard decisions; convolving the at least one additional harddecisions with the selected plurality of interference cancellationfilter taps thereby generating at least one additional convolved signal;and subtracting the at least one additional convolved signal with atleast one additional delayed version of the signal to generate at leastone additional cleaned signal.
 42. The method of claim 41, furthercomprising: despreading the at least one additional cleaned signalthereby making at least one additional plurality of output softdecisions; and slicing the at least one additional output soft decisionsthereby making at least one additional plurality of output harddecisions.
 43. The method of claim 42, further comprising comparing adifference between the plurality of output hard decisions and the atleast one additional plurality of output hard decisions with apredetermined threshold; and selecting the plurality of output harddecisions when the predetermined threshold exceeds the difference. 44.The method of claim 39, wherein the signal comprises a synchronous codedivision multiple access signal.
 45. The method of claim 39, furthercomprising: estimating a rotation within the plurality of softdecisions; and derotating the plurality of soft decisions according tothe rotation estimate before slicing the plurality of soft decisions.46. The method of claim 45, further comprising rerotating the pluralityof hard decisions according to the rotation estimate.
 47. The method ofclaim 39, wherein the method is performed within at least one of amulti-channel headend physical layer burst receiver, a base stationreceiver, a mobile receiver, a satellite earth station, a towerreceiver, a high definition television set top box receiver, and aBluetooth™ operable device.
 48. The method of claim 39, wherein themethod is performed within a headend physical layer burst receiver. 49.The method of claim 48, wherein the headend physical layer burstreceiver is communicatively coupled to a cable modem termination systemmedium access controller.
 50. The method of claim 39, wherein the methodis performed within at least one of a cable modem termination system anda transceiver.
 51. A successive interference canceling method for codedivision multiple access, the method comprising: despreading a signalthat comprises inter-code-interference thereby making a plurality ofsoft decisions; slicing the plurality of soft decisions thereby making aplurality of hard decisions; re-spreading the plurality of harddecisions; convolving the hard decisions with a selected plurality ofinterference cancellation filter taps thereby generating a convolvedsignal, the selected plurality of interference cancellation filter tapsbeing comprising a plurality of interference cancellation filter tapsthat excludes a first filter tap; subtracting the convolved signal witha delayed version of the signal to generate a cleaned signal;despreading the cleaned signal thereby making at least one additionalplurality of soft decisions; slicing the at least one additionalplurality of soft decisions thereby making at least one additionalplurality of hard decisions; re-spreading the at least one additionalplurality of hard decisions; convolving the at least one additional harddecisions with the selected plurality of interference cancellationfilter taps thereby generating at least one additional convolved signal;subtracting the at least one additional convolved signal with at leastone additional delayed version of the signal to generate at least oneadditional cleaned signal; despreading the at least one additionalcleaned signal thereby making at least one additional plurality ofoutput soft decisions; slicing the at least one additional output softdecisions thereby making at least one additional plurality of outputhard decisions; comparing a difference between the plurality of outputhard decisions and the at least one additional plurality of output harddecisions with a predetermined threshold; and selecting the plurality ofoutput hard decisions when the predetermined threshold exceeds thedifference.
 52. The method of claim 51, further comprising: estimating arotation within the plurality of soft decisions; derotating theplurality of soft decisions according to the rotation estimate beforeslicing the plurality of soft decisions; and rerotating the plurality ofhard decisions according to the rotation estimate.
 53. The method ofclaim 51, further comprising: estimating a rotation within the at leastone additional plurality of soft decisions; derotating the at least oneadditional plurality of soft decisions according to the rotationestimate before slicing the at least one additional plurality of softdecisions; and rerotating the at least one additional plurality of harddecisions according to the rotation estimate.
 54. The method of claim51, wherein the method is performed within at least one of amulti-channel headend physical layer burst receiver, a base stationreceiver, a mobile receiver, a satellite earth station, a towerreceiver, a high definition television set top box receiver, and aBluetooth™ operable device.
 55. The method of claim 51, wherein themethod is performed within a headend physical layer burst receiver. 56.The method of claim 55, wherein the headend physical layer burstreceiver is communicatively coupled to a cable modem termination systemmedium access controller.
 57. The method of claim 51, wherein the methodis performed within at least one of a cable modem termination system anda transceiver.